1. Field of the Invention
The invention relates to a sprocket assembly for mining machines and the like, and more particularly to an adjustable sprocket assembly by which slack may be imparted to or taken up in the one or more chains engaged by the sprocket assembly.
2. Description of the Prior Art
The sprocket assembly of the present invention may have many uses in situations wherein it is desirable to provide an adjustable sprocket assembly to take up or impart slack in one or more chains engaged by the sprocket assembly. For purposes of an exemplary showing, the sprocket assembly of the present invention will be described in its use on a non-oscillating drum-type mining machine having one or more trim chains.
A typical non-oscillating drum-type mining machine comprises a self-propelled vehicle having a centrally located conveyor means for the material being mined. At the forward end of the machine one or more movable beams support a horizontally oriented cutting drum. The cutting drum bears a plurality of cutting tools usually oriented on the cutting drum in a pattern comprising two oppositely oriented helices which are directed toward the center of the drum. This aids in conducting the cut material toward the center of the mining machine and the conveyor forming a part thereof.
Through appropriate drive mechanism and gearing, in association with the beam or beams, the drum is caused to rotate about its axis to produce a cutting action. In the usual practice, the machine is brought to the face of the material being cut and the drum is sumped into the face of the material at the top thereof. Thereafter, through the agency of the beam or beams, the rotating drum is caused to move downwardly, making a complete vertical cut at the face of the material. This procedure is repeated and the mine entry is thereby advanced.
At the position or positions where the drum is supported on one or more beams, the drum cannot carry cutting tools. Therefore, one or more trim chains are required to fill in these one or more positions. The typical trim chain comprises an endless chain made up of cutting tool carrying links and connecting links. The cutting tools are so arranged on the chain as to cut clearance for that portion of the drum not provided with cutting tools.
While not always the case, the trim chains are driven by sprocket means in association with the drum and pass about an idler sprocket assembly mounted on the mining machine at the other end of the trim chain flight.
During its assembly on or removal from the mining machine, it is necessary that a trim chain be slack. In addition, during continued use, the chain links and pintles joining them become worn causing the effective length of the chain to increase. It is therefore necessary that the mining machine have some means to provide and to take up slack in the one or more trim chains mounted thereon. To this end, prior art workers have developed a number of types of adjustable idler sprockets supporting the one or more trim chains at the rearward end of the chain flight.
For example, in a mining machine of the type having two supporting booms and a trim chain for each boom, prior art workers have developed a sprocket assembly comprising a non-rotating shaft. The shaft ends terminate in portions supported in ways in the mining machine body. The shaft extends transversely of the mining machine body and substantially parallel to the cutting drum. The shaft is slidable in its supporting ways longitudinally of the mining machine (i.e. toward and away from the cutter drum) whereby slack may be purposely introduced into or taken up from the trim chains supported by the sprocket assembly.
A sprocket is rotatively mounted adjacent each end of the shaft on suitable bearing means. Each sprocket supports one of the two trim chains and constitutes an idler sprocket therefor. The central portion of the shaft, between the two sprockets, passes through a housing. A cylinder and piston are oriented at right angles to the shaft axis. The forward end of the piston is adapted to contact the shaft at its longitudinal center. When grease under pressure is introduced into the cylinder, it will cause the piston to shove the shaft and entire sprocket assembly rearwardly of the mining machine in the supporting ways. When the desired adjusted position of the sprocket assembly has been attained, it is usual to pin the shaft ends in the ways so as to lock the sprocket assembly in its adjusted position.
In other embodiments, prior art workers have used screw-down means to contact the center of the shaft of the sprocket assembly to shift the sprocket assembly to a desired adjusted position.
These prior art adjustable sprocket structures have been characterized by certain inherent deficiencies. First of all, since the sprocket assembly during adjustment is shoved rearwardly at its longitudinal center, it tends to teeter about the piston or screw-down means engaging it. This makes precise adjustment of the sprocket assembly difficult. In addition, the sprocket assembly can skew which, in time, will cause the seals of the sprocket assembly to fail and the bearings thereof to become worn. Furthermore, the pins locking the ends of the shaft of the sprocket assembly in the ways are loaded in shear which again is undesirable and may result in failure of the pins.
The present invention is directed to an adjustable sprocket assembly which, unlike prior art structures, may be assembled from its center so that the adjustment means for shifting the sprocket assembly to its desired position may be located at the outboard ends of the sprocket assembly. This enables precise adjustment of the sprocket assembly for the removal of trim chain slack and eliminates uncontrollable teeter or skewing of the assembly. To hold the assembly in its desired adjusted position, the present invention contemplates the use of washer-like spacer means which are loaded in compression and not subjected to shear stresses. The sprocket assembly of the present invention is hydraulically actuated, simple in construction and may be designed to carry one or more trim chains, and one or more sets of sprocket teeth, all as will be described hereinafter.